On-chip embedded oscillators (or resonators) with high signal quality (signal to noise ratio) can enable energy efficient building blocks for computing and communications. However, existing solutions for on-chip embedded oscillators suffer from large footprint, and/or high operating power. These issues may limit or significantly constrain the design space for processors e.g., wireless SoCs (System on Chips).
Spin torque oscillators (STOs) provide a feasible solution to embedded nano-scale oscillators. One example of an STO is described with reference to FIG. 1. FIG. 1 illustrates STO 100 which consists of fixed and free ferromagnets (e.g., Co) sandwiched between non-magnetic layers (e.g., Cu) as shown. The fixed and free magnets together with the non-magnetic layers form a magnetic junction. If the non-magnetic layer between the ferromagnetic layers is a tunneling dielectric, the stack of layers is referred to as Magnetic Tunneling Junction (MTJ). When voltage VE is applied across the upper and lower non-magnetic layers of STO 100, current ‘I’ flows through STO 100. In this example, an external magnetic field bias ‘B’ is applied to cause STO 100 to oscillate. However, STO 100 is limited.
For example, STO 100 has a high operating power requirement due to large bias current (e.g., greater than 100 μA) and voltage VE (e.g., greater than 0.7 V) requirements of tunnel junction based MTJ. STO 100 also suffers from reliability issues due to high tunneling current in the MTJ. STO 100 uses external magnetic bias ‘B’ to operate as a self-sustained oscillator. This external magnetic bias ‘B’ is an additional cost and may introduce noise in signals on the processor. STO 100 also lacks an efficient coupling mechanism between individual oscillating elements.